This application aims to elucidate the molecular mechanism by which the two non-enveloped viruses polyomavirus (Py) and SV40 penetrate the endoplasmic reticulum (ER) membrane. To infect cells, Py and SV40 bind to glycolipid receptors called gangliosides on the host cell surface and are internalized. The viruses are then transported to the lumen of the ER where they co-opt host cell machineries to cross the ER membrane and reach the cytosol. From the cytosol, Py and SV40 are transported into the nucleus where transcription and replication of the viral DNA ensue, leading to lytic infection or cell transformation. How these viruses penetrate the ER membrane to reach the cytosol, a decisive infection event, remains mysterious and is a process we intend to clarify in this proposal. PUBLIC HEALTH RELEVANCE: The murine polyomavirus (Py) and SV40 are tumor-causing viruses. A decisive step in their infection pathway is transport of the viruses across the membrane of a sub-cellular compartment known as the endoplasmic reticulum (ER). However, the molecular basis by which Py and SV40 breach the ER membrane remains enigmatic. In this proposal, we intend to elucidate this mysterious process.